If they did some colos as vendor J and some colos as vendor C, I think it would be manageable, but I don't really know how much of the cross colo traffic is actually their routers talking to their routers. Homogeneity in networks makes things easier to manage, until a platform fault breaks everything at the same time. In this case, at least it was related to a change they had made and happened quickly, so it was easy to determine the cause; other platform faults may not be as easy to determine, but if only your vendor X colos fell over, at least you'd have your vendor C colos up and something to look for.